Recently, electromagnetic cooking devices using electromagnetic induction as an energy source have been widely utilized for both business service and home appliances in stead of gas cooking stoves. A heating principle of such an electromagnetic cooling device is such that an induction coil is provided underneath a plate on which cooking containers such as pans, pots, and cooking skillets are placed, an alternating magnetic field generated by such induction coil produces eddy current in the cooking container, then the eddy current flow in the container results in generating heat depending on a specific impedance of material constituting the cooking container.
As described above, it has been conventionally considered that generation of the eddy current in the cooking container by means of the alternating magnetic field requires a magnetic material such as stainless steel, steel or the like (see, Nikkei New Materials, dated Mar. 18, 1991, p.20) for that material of the container.
Therefore, the containers for electromagnetic cooking devices such as pans, pots, and cooking skillets have generally been made of iron metal, or made of clad metal which is superposed with two or more different kinds of metals, for example, stainless steel and aluminum alloy etc.
However in the container made of materials as in the above, the inventors of the present invention has found problems in that, with iron container used, the cooking repeated with heating and cooling in the extremely strong magnetic field disadvantageously provides deformation in such container due to produced magnetostriction, and in addition, tends to cause rust, and makes more weighty.
In the container made of the clad metal, repeat of heating and cooking through the use produces difference of thermal expansion and magnetostriction between the different kinds of metals which are superposed each other, this results in more weight in addition to peeling on bonding of those different kinds of metals.
Furthermore, a unitary bonding of different kinds of metals requires higher costs for scrapping process in addition to a complicated and therefore expensive manufacturing process.
A drawback is that austenite stainless steel arranged on inside surface of the container which contacts with meat or vegetable or the like on cooking tends to scorch and stick to the inside surface of the container.
The present invention has been developed for solving the problems described above. An object of the invention is to provide a container for an electromagnetic cooking device which is easy to handle with light weight and exhibits a high heating-efficiency due to electromagnetic induction and a graded corrosion-resistance without peeling on bonding surface between the different kinds of metals and without deformation even in the repeat use.
Another object of the invention is to provide a method of manufacturing a container of an electromagnetic cooking device which is capable of easily manufacturing the electromagnetic cooking device container having the characteristics as hereinbefore described.